In general, different images are input to the left and right eyes of a viewer and are then combined in the brain of the viewer such that a three-dimensional image is perceived. In order to form such a three-dimensional image, a device for providing different images to the left and right eyes of the viewer is required. Conventionally, a linear polarization display apparatus which uses a pair of three-dimensional glasses for dividing an image into a left-eye image and a right-eye image was used. However, such a linear polarization display apparatus is inconvenient in that the viewer must wear the three-dimensional glasses.
Accordingly, in order to solve such a problem, methods which form a three-dimensional image without using glasses were suggested. In these methods, a three-dimensional image display apparatus is configured by combining a flat display device, such as a liquid crystal display panel (LCD) and a plasma display panel (PDP), and a device for dividing an image by different angles viewed by the viewer. Depending upon the device for dividing the image by the different angles viewed by the viewer, a wide range of methods, such as a lenticular method using a lenticular lens sheet, a parallax barrier method using a slit array sheet, an integral photography method using a micro-lens array sheet, and a holography method using a disturbance effect, can be proposed.
Among them, the parallax barrier method is disadvantageous in that most of light is blocked by slits and thus the brightness of the screen decreases. The integral photography method and the holography method are unlikely to be implemented because a massive amount of data must be processed. Accordingly, recently, the lenticular method is attracting attention.
FIG. 1 is a view showing a conventional three-dimensional image display apparatus using the lenticular method. As shown in FIG. 1, the three-dimensional image display apparatus using the lenticular method includes a flat display device 10 for displaying a plurality of parallax images and a lenticular lens plate 12 provided on the front surface of the flat display device 10. The lenticular lens plate 12 is provided such that the vertical axis thereof is parallel to the vertical axis of the flat display device 10, and is spaced apart from the flat display device 10 by a predetermined distance such that an image is mainly laid on a focus surface of a lenticular lens.
However, the conventional three-dimensional image display apparatus has the following problems.
As shown in FIG. 1, in the conventional three-dimensional image display apparatus using the lenticular method using four images, vertical resolution is equal to that of the parallax images before sampling, but horizontal resolution is reduced to ¼ of the resolution of the parallax images before sampling. That is, as shown in FIG. 2, in the conventional lenticular method, the horizontal resolution is reduced to 1/n (n: number of parallax images).
To obviate the above problems, FIG. 3 is a view showing the resolution of the embodiment of the three-dimensional image display apparatus according to the present invention. In FIG. 6, the lenticular lens 12 is provided such that the vertical axis 16 of the lenticular lens 12 is tilted by the predetermined angle α. A method of improving the horizontal resolution at the sacrifice of the vertical resolution is suggested. In FIG. 7, nine parallax images are used for implementing a three-dimensional image. As shown, the horizontal resolution is reduced to about ⅓ of the resolution of a conventional two-dimensional image, instead of 1/9 of the resolution of the conventional two-dimensional image. However, the vertical resolution is reduced to about ⅓ of the resolution of the conventional method which did not deteriorate. That is, the deterioration of the horizontal/vertical resolution is in balance and thus a viewer feels that image quality is improved compared with the conventional method. At this time, the tilt angle α of the lenticular lens is defined by Equation 1.α=arctan(Hp/VpR)  Equation 1
where, Hp denotes a subpixel period in a horizontal direction, Vp denotes a subpixel period in a vertical direction, and R denotes the number of rows used in an array of plural images, which is an integer of 2 or more.
For example, the lenticular lens plate 12 is tilted such that α becomes 9.4° or 6.3°. A parallelogram 18 shown in FIG. 7 represents unit resolution in the method of tilting the lenticular lens and a rectangle 20 represents unit resolution in a two-dimensional image.
When the three-dimensional image is viewed using the three-dimensional image display apparatus using the lenticular lens method, there is a region for allowing a viewer to optimally view the image, which is called an elementary three-dimensional space. Accordingly, as the size of the elementary three-dimensional space increases, a space for allowing the viewer to normally view the three-dimensional image without pseudoscopic vision expands. The size of the elementary three-dimensional space is represented by the horizontal length L of the elementary three-dimensional space and the horizontal length L is calculated by Equation 2.L=m×d  Equation 2
where, m denotes the number of parallax images included in the elementary three-dimensional image and d denotes the length of the elementary three-dimensional space corresponding to one parallax image.
Accordingly, it can be seen that L must increase in order to increase the size of the elementary three-dimensional space and the number m of parallax images or the length D of the elementary three-dimensional space corresponding to one parallax image must increase in order to increase L. This will be described in detail with reference to FIG. 8. FIG. 8A shows a case where four parallax images are used (m=4) and FIG. 8B shows a case where six parallax images are used (m=6). As can be seen from FIGS. 8A and 8B, L increases if d or m increases and the elementary three-dimensional space expands if L increases.
However, since d must be smaller than a distance between the both eyes of the viewer, there is a limitation in increasing d. Thus, m must increase. However, when m increases, the resolution deteriorates. Accordingly, in the three-dimensional image display apparatus using the lenticular method, the elementary three-dimensional space must expand without deteriorating the resolution.
When the flat display device 10 for displaying the plurality of parallax images is implemented by an LCD in the three-dimensional image display apparatus, the following problems occur. As shown in FIGS. 3A and 3B, as the size of the LCD increases and the LCD and polarization plates (not shown) provided on the front and rear surfaces of the LCD are different from each other in thermal expansion or contraction characteristics, the LCD may be curved forward or backward. In addition, a distance 1 between a three-dimensional filter such as the lenticular lens plate 12 and the flat display device 10 such as the LCD is not uniform over the whole screen and the three-dimensional effect significantly deteriorates.